Mobile radio systems provide a radio access interface via which data can be communicated with mobile units, also called terminals or user equipments (UEs). There are various techniques for communicating data to a plurality of terminals contemporaneously, whilst making most efficient use of an available radio communications bandwidth. Different radio communications systems are typically using different frequency bands which are allocated to different technologies and/or operators. For example, in the frequency bands defined in the 3GPP standard GSM 900, the band 890-894.6 MHz has been allocated in the United Kingdom to Vodafone and the band 894.8-902 MHz to O2. Each operator is then in charge of allocating carrier frequencies to be used in communications where the carrier frequencies are in the band or bands allocated to this operator.
The spectrum can also be divided between technologies available for a standard. For example, the 3G standard defines Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) radio communications and separate parts of the spectrum may be allocated to each of them.
The spectrum is usually divided into different bands that do not overlap each other in order to reduce the risk of interference between signals in these different bands. However, in reality, communications in separate but neighbouring frequency bands may interfere with each other, as a result for example of out of band interference. This interference can cause a significant signal to noise ratio degradation or carrier to interference ratio degradation which effectively causes a loss in capacity to the mobile radio network. A common way of mitigating a reduction in signal quality and/or strength is to increase transmission power. However doing so in the case of interfering radio signals in a mobile radio network can actually increase the interference and can therefore decrease the network's capacity.
In some countries different mobile radio networks and/or different parts of a mobile radio network using different wireless access interfaces are provided with frequency bands which are neighbouring one another. Reducing interference between frequency bands from different wireless access interfaces can therefore represent a technical problem.